The present invention relates to implantable stimulation devices, e.g., cochlear prosthesis used to electrically stimulate the auditory nerve, and more particularly to an electrode array for use with a cochlear stimulator that is designed to monitor the stapedius reflex of a patient.
In International Application Number PCT/US97/10590, filed internationally on Jun. 19, 1997, there is disclosed a self-adjusting cochlear implant system, and a method for fitting such a system, that relies, in part, on sensing the stapedius reflex of the patient. This PCT application (PCT/US97/10590) is incorporated herein by reference.
The stapedius reflex is used in cochlear implants to determine how much sound energy a patient perceives. This information is very useful in programming the cochlear implant system so that proper signal levels may be maintained. Thus, as is described in the referenced PCT application, an implantable electrode placed over or in the stapedius muscle, in conjunction with the reverse telemetry features of the implantable cochlear stimulator (ICS), which allow sensed data to be telemetered from an ICS to an external unit, provide a very useful tool to enhance the programming of the ICS.
The stapedius reflex operates in a normal ear to dampen movement of the ossicular chain, and in particular the stapes, so that excessive motion of the stapes (which could otherwise be sensed as an extremely-loud, potentially-damaging, sound) is not transmitted through the oval window into the inner ear.
Unfortunately, sensing the stapedius reflex is not an easy task. This is because the stapedius muscle, which is attached to the stapes, is hidden inside a bony channel, and only a very small part of it and its tendon are visible and/or accessible from within the middle ear. Further, because only a very small part of the muscle is accessible, it is difficult to attach an electrode to the stapedius reflex muscle without damaging the integrity of the stapedius reflex muscle.